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Editorial

ASME J of Medical Diagnostics. 2018;1(3):030201-030201-2. doi:10.1115/1.4040388.
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Translational research is an essential component of the scope of the ASME Journal of Engineering and Science in Medical Diagnostics and Therapy. Turning insights from multidisciplinary research into diagnostic or therapeutic methods and tools/procedures is the optimum goal of the journal. This issue includes a range of research which fulfils these objectives.

Commentary by Dr. Valentin Fuster

Research Papers

ASME J of Medical Diagnostics. 2018;1(3):031001-031001-6. doi:10.1115/1.4039560.

We found a significant difference (P < 0.05) between the linear portion of the elastic modulus (∼20 MPa) and tensile strength (∼2 MPa) at the 0.2 mm/s (low: 0.01 s−1), 2 mm/s (medium: 0.11 s−1), and 20 mm/s (high: 1.11 s−1) loading rates by performing a series of uniaxial stretching tests. However, the mechanical properties of the neural fiber bundles were resultantly of the same magnitude, indicating that their mechanical responses were relatively insensitive to a given strain rate regardless of a 100-fold increase in the applied stretching velocities. We also confirmed that a “spinal level effect” exists in the nerve roots, i.e., a fiber bundle isolated from the lumbar spinal level is weaker in mechanical strength compared to that from the cervical and thoracic spinal levels (P < 0.05), suggesting that closer attention should be paid to an anatomical site from which test samples are excised.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2018;1(3):031002-031002-11. doi:10.1115/1.4039661.

Instrument-assisted soft tissue manipulation (IASTM) is a form of manual therapy which is performed with rigid cast tools. The applied force during the IASTM process has not been quantified or regulated. Nor have the angle of treatment and strokes frequency been quantified which contribute to the overall recovery process. This paper presents a skin modeling analysis used in the design of a novel mechatronic device that measures force in an IASTM application with localized pressures, similar to traditional, nonmechatronic IASTM devices that are frequently used to treat soft tissue dysfunctions. Thus, quantifiable soft tissue manipulation (QSTM) represents an advancement in IASTM. The innovative mechatronic QSTM device is based on one-dimensional (1D) compression load cells, where only four compression force sensors are needed to quantify all force components in three-dimensional (3D) space. Here, such a novel QSTM mechatronics device is simulated, analyzed, and investigated using finite element analysis (FEA). A simplified human arm was modeled to investigate the relationship between the measured component forces, the applied force, and the stress and strain distribution on the skin surface to validate the capability of the QSTM instrument. The results show that the QSTM instrument as designed is able to correlate the measured force components to the applied tool-tip force in a straight movement on the skin model.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2018;1(3):031003-031003-10. doi:10.1115/1.4040001.

Volatile anesthetics have been shown to reduce lung resistance through dilation of constricted airways. In this study, we hypothesized that diffusion of inhaled anesthetics from airway lumen to smooth muscle would yield significant bronchodilation in vivo, and systemic recirculation would not be necessary to reduce lung resistance (RL) and elastance (EL) during sustained bronchoconstriction. To test this hypothesis, we designed a delivery system for precise timing of inhaled volatile anesthetics during the course of a positive pressure breath. We compared changes in RL, EL, and anatomic dead space (VD) in canines (N = 5) during pharmacologically induced bronchoconstriction with intravenous methacholine, and following treatments with: (1) targeted anesthetic delivery to VD and (2) continuous anesthetic delivery throughout inspiration. Both sevoflurane and isoflurane were used during each delivery regimen. Compared to continuous delivery, targeted delivery resulted in significantly lower doses of delivered anesthetic and decreased end-expiratory concentrations. However, we did not detect significant reductions in RL or EL for either anesthetic delivery regimen. This lack of response may have resulted from an insufficient dose of the anesthetic to cause bronchodilation, or from the preferential distribution of air flow with inhaled anesthetic delivery to less constricted, unobstructed regions of the lung, thereby enhancing airway heterogeneity and increasing apparent RL and EL.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2018;1(3):031004-031004-14. doi:10.1115/1.4040055.

Efficient management of operating room (OR) schedules is important as the OR is the largest cost and revenue center in a hospital and can substantially impact its staffing and finances. A major problem associated with developing OR schedules for elective surgeries is the schedule disruption from uncertainty inherent in the duration of surgical services. Another problem is the cascaded impact on overall system performance of facilities and resources upstream and downstream to the OR. Using a manufacturing system analytical approach, the peri-operative process is modeled as a transfer line with three machines and two buffers by a discrete time Markov chain. Uncertain surgical and recovery duration is quantified probabilistically and incorporated in the Markov chain model with multistate geometrical machines. Model predictive control (MPC) to pace patient release into the ORs is then applied to control system transient performance. With this model and empirical studies of surgery and recovery duration, guidance can be given to OR managers on how to dynamically schedule and reschedule patients throughout an OR's day that minimizes cost for a given workload. The proposed predictive control model can also control other transient performance metrics such as OR and recovery room (RR) utilization, patient flow, and cost.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2018;1(3):031005-031005-8. doi:10.1115/1.4040103.

An intracochlear lead-zirconate-titanate (PZT) microactuator integrated with a cochlear implant electrode array could be a feasible strategy to implement combined electric and acoustic stimulation inside the cochlea. The purpose of this paper is to characterize in vitro a prototype PZT microactuator for intracochlear applications, including service life, failure mechanisms, and lead leaching. PZT microactuators were driven sinusoidally to failure in air and in artificial perilymph. Frequency response functions (FRFs) and electrical impedance were monitored. After the PZT microactuators failed, the amount of leached lead was measured via inductive coupled plasma mass spectrometry (ICP-MS). Two failure mechanisms are identified: electrical breakdown and structural failure. The electrical breakdown, possibly from loss of parylene encapsulation, is evidenced by a sudden and significant drop of the actuators' electrical resistance. The structural failure, possibly from electrode delamination, is evidenced by a sudden and significant drop of FRFs. The amount of lead leached from the PZT microactuator is well below published safety guidelines from federal agencies.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2018;1(3):031006-031006-12. doi:10.1115/1.4040145.

Cancerous tissues are known to possess different poroelastic properties with respect to normal tissues. Interstitial permeability is one of these properties, and it has been shown to be of diagnostic relevance for the detection of soft tissue cancers and for assessment of their treatment. In some cases, interstitial permeability of cancers has been reported to be lower than the surrounding tissue, while in other cases interstitial permeability of cancers has been reported to be higher than the surrounding tissue. We have previously reported an analytical model of a cylindrical tumor embedded in a more permeable background. In this paper, we present and analyze a poroelastic mathematical model of a tumor tissue in cylindrical coordinate system, where the permeability of the tumor tissue is assumed to be higher than the surrounding normal tissue. A full set of analytical expressions are obtained for radial displacement, strain, and fluid pressure under stress relaxation testing conditions. The results obtained with the proposed analytical model are compared with corresponding finite element analysis results for a broad range of mechanical parameters of the tumor. The results indicate that the proposed model is accurate and closely resembles the finite element analysis. The availability of this model and its solutions can be helpful for ultrasound elastography applications such as for extracting the mechanical parameters of the tumor and normal tissue and, in general, to study the impact of poroelastic material properties in the assessment of tumors.

Commentary by Dr. Valentin Fuster
ASME J of Medical Diagnostics. 2018;1(3):031007-031007-8. doi:10.1115/1.4040199.

Dynamic elastography methods attempt to quantitatively map soft tissue viscoelastic properties. Application to the fingertip, relevant to medical diagnostics and to improving tactile interfaces, is a novel and challenging application, given the small target size. In this feasibility study, an annular actuator placed on the surface of the fingertip and driven harmonically at multiple frequencies sequentially creates geometrically focused surface (GFS) waves. These surface wave propagation patterns are measured using scanning laser Doppler vibrometry. Reconstruction (the inverse problem) is performed in order to estimate fingertip soft tissue viscoelastic properties. The study identifies limitations of an analytical approach and introduces an optimization approach that utilizes a finite element (FE) model. Measurement at multiple frequencies reveals limitations of an assumption of homogeneity of material properties. Identified shear viscoelastic properties increase significantly as frequency increases and the depth of penetration of the surface wave is reduced, indicating that the fingertip is significantly stiffer near its surface.

Commentary by Dr. Valentin Fuster

Expert View

ASME J of Medical Diagnostics. 2018;1(3):034701-034701-7. doi:10.1115/1.4039561.

The use of reference ranges is well established in medical practice and research. Classically, a range would be derived from the local healthy population and matched in age, gender, and other characteristics to the patients under investigation. However, recruiting suitable controls is problematic and the derivation of the range by excluding 2.5% at each end of the distribution results in 5% of the values being arbitrarily discarded. Thus, the traditional reference range is derived using statistical and not clinical principles. While these considerations are recognized by clinicians, it is often not realized that the application of whole population derived reference ranges to complex pathologies that comprise patient subgroups may be problematic. Such subgroups may be identified by phenotypes including genetic etiology, variations in exposure to a causative agent, and tumor site. In this review, we provide examples of how subgroups can be identified in diverse pathologies and how better management can be achieved using evidence-based action limits rather than reference ranges. We give examples from our clinical experience of problems arising from using the wrong reference ranges for the clinical situation. Identifying subgroups will often enable clinicians to derive specific action limits for treatment that will lead to customized management and researchers a route into the study of complex pathologies.

Commentary by Dr. Valentin Fuster

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